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Divers continued their search for survivors from the Italian cruise ship Saturday, as concerns grow over the potential environmental threat posed by the wreck.

A 12th body was found within the ship Saturday afternoon, Italian authorities confirmed, with at least 20 people still missing since the Costa Concordia ran aground off the island of Giglio last week.

The body of a woman wearing a life jacket was discovered in an area of the ship that was under water, said Francesca Maffini, spokeswoman for Franco Gabrielli, the individual in charge of operations at the site.

A committee made up of all the parties involved in the rescue operation told a briefing for reporters and villagers on the island that search and rescue efforts will continue -- but that the environmental risk is also becoming urgent.

Officials said they cannot predict how long it will take to clear the wreckage, since that depends on maritime conditions and technical difficulties, but that all legal, environmental and human factors will be taken into account.

"It's time for Italy to show it can do something right and do it well," Gabrielli said.

Gabrielli, who leads Italy's civil protection agency, warned that the task ahead was complicated and daunting, not least because it takes about 45 minutes to search each cabin, using special cameras and divers.

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Gabrielli said no fuel oil had yet leaked from the ship -- only kitchen and engine oil -- and that he did not see an immediate risk of the 2,400 tons on board escaping.

A plan to remove the fuel oil has now been approved, he said, and will begin once experts give the go-ahead.

Booms have been put in place around the ship to try to stop the spread not just of oil but of many other pollutants, from detergents to sewage chemicals. With 4,000 people aboard, the ship was the size of a small town, Gabrielli said.

Adm. Ilarione Dell'Anna, head of coastal authorities for the port city of Livorno, said fuel will be replaced with water as it is removed from the ship's tanks, to keep the ship balanced.

Gabrielli said Costa Cruises, the company that owns the cruise ship, was being very cooperative and was proving responsible, despite past errors.

Both Costa Cruises and authorities have criticized Capt. Francesco Schettino, who is under house arrest and faces possible charges of manslaughter, shipwreck and abandoning ship.

An audio recording obtained by Italy's Repubblica newspaper and published Saturday shows that the captain, at least at the outset of the incident, assured authorities he would do the right thing.

According to the recording, an Italian Coast Guard official asks Schettino how many people still needed to be evacuated to the top of the ship to be rescued on life boats.

"About two of three hundred people still," the captain says.

The Coast Guard asks -- will everyone evacuate, or will someone stay behind?

"I will stay here," Schettino answers, saying that he believed that the boat was done leaning over.

Other audio recordings previously released, however, indicate that Schettino did not stay on board, but left the ship, to the chagrin of authorities.

The office of prosecutor Francesco Verusio said it would lodge an appeal Saturday at a court in Florence against the investigating judge's decision to grant the captain house arrest.

Verusio has said he that the captain should be in jail given the flight risk, and the gravity of his crimes.

Schettino's lawyer, Bruno Leporatti, spoke to Italian news channel Sky Tg24 on Friday, urging people to reserve judgment on the captain until they have all the facts.

Schettino's leadership has been repeatedly questioned. Earlier this week, a cook from the ship told a Filipino television station that the captain ordered dinner for himself and a woman at about 10:30 p.m. -- less than an hour after the collision.

However, a Moldovan woman, Domnica Cemortan, 25, who also works for the cruise line but said she was on the Concordia as a passenger, defended the captain in a TV interview.

"I've heard in Russian media that the captain left the ship first, or among the first. But this is not true," she said.

The cruise ship ran aground off the Tuscan coast on January 13, and it appears increasingly unlikely that any survivors will be found.

Eight of the dead have so far been named -- four French passengers, a Spanish passenger, an Italian, along with a Hungarian crew member and a Peruvian crew member.

Prosecutors have accused the captain of piloting the ship too fast to allow him to react to dangers, causing the shipwreck, according to legal papers.

Judge Valeria Montesarchio's initial ruling found Schettino changed the ship's course, steering too close to shore and causing the ship to hit a rock.

Earlier this week, Costa Cruises chairman Pier Luigi Foschi placed the blame for the wreck squarely on the captain, saying it was his choice to deviate from frequently traveled routes.

There were roughly 4,200 people on the Costa Concordia when it ran aground -- about 3,200 passengers and 1,000 crew members. The vast majority fled the ship safely.